add open graph and twitter card meta tags

Product pages get og:type=product, og:url, og:image (hero image), and
twitter:card=summary_large_image. All other shop pages get og:type=website
and twitter:card=summary. og:title and og:description mirror the existing
page title and meta description.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/berrypod_web/live/shop/product_show.ex

@@ -52,6 +52,9 @@ defmodule BerrypodWeb.Shop.ProductShow do
           socket
           |> assign(:page_title, product.title)
           |> assign(:page_description, meta_description(product.description))
+          |> assign(:og_type, "product")
+          |> assign(:og_url, BerrypodWeb.Endpoint.url() <> "/products/#{slug}")
+          |> assign(:og_image, og_image_url(all_images))
           |> assign(:product, product)
           |> assign(:all_images, all_images)
           |> assign(:gallery_images, gallery_images)
@@ -216,6 +219,9 @@ defmodule BerrypodWeb.Shop.ProductShow do
     """
   end
 
+  defp og_image_url([%{url: "/" <> _ = path} | _]), do: BerrypodWeb.Endpoint.url() <> path
+  defp og_image_url(_), do: nil
+
   defp meta_description(nil), do: nil
 
   defp meta_description(text) do